Fair Value Measurements: Schedule of estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in equity securities, at fair value	$ 850	$ 835
Other investments, at cost	3,000	3,000	[1]
Recorded Amount
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	142,483	316,755
CDs held for investment	20,168	22,894
Investment securities	332,749	308,023
Investments in equity securities, at fair value	850	835
FHLB stock	2,202	2,194
Other investments, at cost	3,000	3,000
Loans held for sale	200	748
Loans receivable, net	1,210,193	1,132,426
Accrued interest receivable	5,295	4,483
Certificates of deposit	186,109	122,584
Accrued interest payable	500	108
Fair Value
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	142,483	316,755
CDs held for investment	20,168	22,519
Investment securities	319,930	291,198
Investments in equity securities, at fair value	850	835
FHLB stock	2,202	2,194
Other investments, at cost	3,000	3,000
Loans held for sale	204	758
Loans receivable, net	1,171,041	1,124,579
Accrued interest receivable	5,295	4,483
Certificates of deposit	183,424	120,807
Accrued interest payable	500	108
Fair Value | Fair Value, Inputs, Level 1
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	142,483	316,755
CDs held for investment	20,168	22,519
Investment securities	162,022	158,578
Investments in equity securities, at fair value	850	835
FHLB stock	2,202	2,194
Other investments, at cost	3,000	3,000
Loans held for sale	204	758
Loans receivable, net	0	0
Accrued interest receivable	5,295	4,483
Certificates of deposit	0	0
Accrued interest payable	500	108
Fair Value | Fair Value, Inputs, Level 2
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
CDs held for investment	0	0
Investment securities	157,908	132,620
Investments in equity securities, at fair value	0	0
FHLB stock	0	0
Other investments, at cost	0	0
Loans held for sale	0	0
Loans receivable, net	0	0
Accrued interest receivable	0	0
Certificates of deposit	0	0
Accrued interest payable	0	0
Fair Value | Fair Value, Inputs, Level 3
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
CDs held for investment	0	0
Investment securities	0	0
Investments in equity securities, at fair value	0	0
FHLB stock	0	0
Other investments, at cost	0	0
Loans held for sale	0	0
Loans receivable, net	1,171,041	1,124,579
Accrued interest receivable	0	0
Certificates of deposit	183,424	120,807
Accrued interest payable	$ 0	$ 0

[1] Derived from audited consolidated financial statements.